1. Field of the Invention
The present invention relates to the class of devices known as optical waveguides and in particular to polymer optical waveguides for use in optical communication with near infrared light.
2. Description of the Related Art
In optical waveguides formed of an optical polymer which has low light loss in the optical communication wavelength region containing the near infrared region, it is necessary to minimize light scattering loss at the boundary between core and cladding of the waveguide. In order to minimize light scattering loss, when etching an optical waveguide it is imperative to appropriately control parameters such as the uniformity of a side wall of an etched waveguide, the vertical profile of the side wall and the etch rate. Since such parameters are directly affected by the plasma density and ion energy during etching and are optimized under contrary conditions, the plasma density and the ion energy must be independently controlled. Particularly, in the case of etching an optical waveguide formed of polymer containing halogen atoms, it is important to reduce damage in an optical waveguide by increasing the etch rate to minimize the exposure to the plasma. Again, it is necessary to independently control the plasma density and ion energy.
A general method for fabricating an optical waveguide will now be described. First, a lower cladding layer is formed on a substrate and then a core layer is formed on the lower cladding layer. Subsequently, a photoresist layer is formed on the core layer, exposed and then developed the resultant, to form a photoresist pattern. The core layer is etched using a photoresist pattern and then patterned. Then, an upper cladding layer is formed on the patterned core layer, thereby completing the optical waveguide.
As an etching method of the core layer, a reactive ion etching (RIE) method is widely used, in view of processing stability, preciseness and productivity. However, with the RIE method, the etch rate is very low, i.e., not more than 500 nm/min, which causes the substrate to be exposed to plasma for a long time to be damaged. In addition to damage to the etched plane, the vertical profile of the etched plane is nonuniform. And, in the case of increasing the plasma density for the purpose of enhancing the etch rate, the ion energy increases, which causes to damage the etched plane. Conversely, in the case of decreasing the plasma density for the purpose of reducing damage to the etched plane, the etch rate is lowered, and the substrate is exposed to the plasma for a long time, bringing about film damage.
Based on our observation of the art, we have observed that what is needed is a polymer optical waveguide which does not suffer from plasma damage during the manufacturing process. Specifically, a composition and a manufacturing method are needed which will allow a high etch rate without damage to the optical waveguide.